Method for cast moulding contact lenses with a rounded edge form

ABSTRACT

Methods for producing contact lenses include providing a back surface tool having a surface generally corresponding to a desired contact lens surface and a convex curve along an outer radius thereof, positioning the tool in a molding apparatus, introducing a moldable material into the molding apparatus to form a first mold section having a negative impression of the surface of the tool, assembling the first mold section with a second mold section to form a lens shaped cavity therebetween and forming a contact lens member in the lens shaped cavity of the assembled mold sections. Molds useful in producing contact lenses, tools useful in making mold sections for molding contact lenses and contact lenses having rounded edge surfaces are also provided.

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to the manufacture ofcontact lenses and more specifically relates to methods for cast moldingcontact lens with a molded edge that requires no dedicatedpost-processing steps.

[0002] Contact lenses have historically been made by machining a lensmaterial, in button (or block) form on front and back surfaces thereofto produce an unfinished lens product having the required fit, or “basecurve”, and visual correction, to compensate for one or more refractiveabnormalities of the eye. Such refractive abnormalities may includemyopia (nearsightedness), hypermetropia (farsightedness), astigmatism,presbyopia and the like. Using conventional machining technology, theoptic faces of the unfinished lens require polishing in order to removerings, known as “turning rings”, on the unfinished lens that have beencreated by the machining process. Typically the edge of the lens is alsopolished to produce smooth edge geometry, or profile, in order tomaximize wearer comfort and prevent injury to the eye. The edgepolishing step is particularly important in the manufacture of “hard”lenses, in which the lens material is relatively rigid and inflexibleand even small defects on the edge can cause irritation in the wearers'eye.

[0003] The machining process described above, being very laborintensive, has been widely replaced by cast molding of the lens. Inconventional cast molding techniques, front and back surface mold halvesare made for the required lens prescription. Each mold section isproduced by injection molding techniques. A mold insert tool, forexample made of metal, ceramic or the like, is provided and secured orfixed in an injection molding machine. A mold section, or mold half, isthen produced having the contour of the insert. Thus, the mold sectionmay include a negative impression of, or a contour which corresponds to,the desired lens front or back surface.

[0004] The two mold halves are assembled and lens material, for examplea curable, mixture of polymerizable monomers, is introduced between theassembled mold halves. After the cast molding steps, subsequentprocessing steps are employed, which may include for example, curing,demolding, hydration (in the case of hydrogel lenses). In addition, edgepolishing operations are often performed to smooth the edge profile ofthe lens.

[0005] A method of cast molding contact lenses, particularly toriccontact lenses, is described in Appollonio, et al, U.S. Pat. No.5,611,970 which is incorporated in its entirety herein by reference.

[0006] Methods for fully cast molding contact lenses have beendeveloped. Fully cast molded lenses are lenses in which all surfaces,front, back and edge of the lens are molded as part of a mold pair andno post processing polishing or machining operations are performed toyield the final lens product.

[0007] Unfortunately, although fully molded lenses provide aninexpensive and flexible alternative to machined and polished castmolded lenses, fully molded lenses are sometimes uncomfortable for thewearer and may even harm the eye, particularly after long term use.

[0008] It has been shown that the form and size of the edge of a contactlens have significant effects on wearer comfort and conjunctival heath.It is conventional that a fully molded lens will have a lens edge formwhich is “chiseled”, or “pointed” in some way, and is not representativeof a polished edge or an edge which had been historically manufacturedto improve wearer comfort.

[0009] Wearers of conventional fully molded lenses have been known tosuffer from eye irritation and reduction in “end of day comfort” of theeye. Moreover, long term wearers have been observed, with the use of afluorescein dye, to have ‘scuff’ marks formed on the sclera, the scuffmarks being caused by interaction between the lens and eye. To achieve amore desirable edge geometry and provide a more comfortable lens, somelens manufacturers will apply additional, separate, post processingsteps such as edge polishing, in otherwise fully molded lenses.Polishing the cast molded lens will generally remove the chiseled orpointed edge profile that is conventionally produced by cast molding.Understandably, however, the additional manufacturing step will tend toincrease the cost of the final lens product.

[0010] It would be highly advantageous to provide a method by which alens could be cast molded, the resulting lens having a desirable,substantially smooth or rounded edge geometry, without the need for postprocessing polishing steps.

SUMMARY OF THE INVENTION

[0011] Accordingly, a method is provided for fully cast molding contactlenses having rounded edge surfaces. Advantageously, by implementationof the present invention, lenses can be created with an edge formproviding enhanced comfort and/or safety without the need for costly andtime consuming post formation processing steps.

[0012] Generally, methods for producing contact lenses, in accordancewith the present invention comprise providing a tooling insert or tool,for example, a back surface tool, having a surface generallycorresponding to a desired contact lens surface and a convex curve alongan outer or peripheral radius thereof. The tool is used to form a moldsection which generally defines a negative impression of a surface ofthe final lens product. For example, the tool is positioned in a moldingapparatus, such as a molding apparatus of conventional design. Amoldable composition, such as a polymeric material or a precursorcomposition of a polymeric material, is introduced into the moldingapparatus and subjected to conditions effective to form a mold sectionhaving a negative impression of the surface of the tool. The moldsection formed by the tool is a back surface mold section. In otherwords, the surface of the tool generally corresponds to a face,preferably the posterior face, of the contact lens to be formed. Thus,the tool may be a back surface tool generally defining the base curve ofthe contact lens product. As will be described in more detailhereinafter, the convex curve of the tool, when used to form a backsurface mold section, provides a contact lens having the desired roundededge form without the need for post formation processing steps.

[0013] For example, to form the rounded edge contact lens, the backsurface tool having the convex curve along the outer radius thereof ispositioned in a molding apparatus, for example, a conventional,injection molding apparatus. A first mold section having a negativeimpression of the surface of the tool is formed. This first mold sectionis assembled with a second mold section. The second mold section may bemade in a conventional manner and preferably generally defines anegative impression of a front, or anterior, surface of the contact lensto be produced. The assembled first and second mold sections form alens-shaped cavity, and the method includes forming a contact lensmember in the lens shaped cavity of the assembled mold sections. Upondemolding or removal from the mold sections, a fully molded, contactlens member having a rounded edge form or surface is obtained.

[0014] The demolded contact lens member may be the final contact lens.However, the demolded contact lens member may be hydrated or furtherhydrated to form the final contact lens with a rounded edge surface. Oneimportant advantage of the present invention is that the present contactlenses preferably do not require post-formation (after being molded)processing to alter the rounded configuration of the outer peripheraledge surface of the contact lens member or contact lens. Post-formationprocessing such as demolding, hydration, sterilization, packaging andthe like of the contact lens or contact lens member does not alter thisrounded edge surface configuration.

[0015] The portion of the back surface tool that forms the lensperiphery is convex in form, preferably having a radius of at leastabout 0.05 mm or larger. Correspondingly, the first mold section formedby the tooling insert has a concave outer edge surface. It will beappreciated by those skilled in the art that both the tooling insert andthe mold section formed thereby, in accordance with the presentinvention, are significantly different in form from conventional backsurface tooling inserts and conventionally produced back surface moldsections.

[0016] Preferably, in accordance with the present invention, a junctionangle formed between the assembled first and second mold sections, onthe lens side of the lens-shaped cavity, is at least about 100 degrees,more preferably in the range of about 100 degrees to about 170 degrees.

[0017] The present invention further provides a tool, preferably a backsurface tool, useful for cast molding a contact lens, for example, acontact lens having a rounded peripheral edge surface in making a moldsection. In accordance with this embodiment of the invention, the toolgenerally comprises an insert adapted to be placed in a moldingapparatus in forming a first mold section, specifically a back surfacemold section, having a negative impression of a surface of the tool. Toform the rounded edge surface of the final lens product, the surface ofthe tool includes a first surface portion in the general shape of a lensface, preferably a posterior lens face, of a contact lens, and a secondsurface portion defining a convex curved outer peripheral edge surfaceof the insert. The second surface portion may be defined by a continuouscurve with a radius of curvature of about 0.05 mm. Alternatively, thesecond surface portion may be defined by a series of small flats, or acombination of small flats and curves, which approximate a convexlycurved surface.

[0018] In another aspect of the present invention, a mold useful inproducing, e.g., cast molding, a contact lens, preferably, a contactlens with a rounded edge surface, is provided. The mold generallycomprises a first mold section having a surface in a general shape of anegative of a lens face, preferably a posterior lens face, of a contactlens to be cast molded using the mold and a concave outer edge surface,and a second mold section having a surface in a general shape of anegative of an opposing lens face, preferably an anterior lens face ofthe contact lens to be cast molded using the mold. The first moldsection and the second mold section are adapted to be assembledtogether, for example, in a conventional manner, to define a cavity, inwhich is formed a fully cast molded, rounded edge contact lens orcontact lens member in accordance with the present invention.

[0019] In a further aspect of the present invention, fully cast moldedcontact lenses having rounded peripheral edge surfaces are provided.Such contact lens may be produced using the methods, tools and moldsdescribed herein.

[0020] It should be appreciated that each and every feature describedherein, and each and every combination of two or more of such features,is included within the scope of the present invention provided that thefeatures included in such a combination are not mutually inconsistent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The advantages of the present invention will be more readilyunderstood with reference to the following description when consideredin conjunction with the appended drawings of which:

[0022]FIGS. 1A and 1B are cross sectional views of conventional moldingsfor forming conventional contact lenses;

[0023] FIGS. 2A-2D are cross sectional views of examples of fully castmolded contact lenses manufactured using conventional moldingtechniques;

[0024]FIG. 3 is a cross sectional view of a fully cast molded contactlens manufactured using a method of the present invention, the contactlens having a substantially smooth, rounded edge profile;

[0025]FIGS. 4A and 4B are sectional and front views of a conventionaltooling insert used in conventional contact lens manufacturingtechniques to form a mold section used for cast molding a contact lens;

[0026]FIG. 5 is a cross sectional view of a fully cast molded contactlens manufactured using another conventional molding technique;

[0027]FIG. 6 is a front view of a tooling insert used in a method of thepresent invention to form a mold section used for cast molding a contactlens with a substantially smooth, rounded edge;

[0028]FIG. 7. is a cross sectional view of the insert of the presentinvention, taken along line 7-7 of FIG. 6; and

[0029]FIG. 8 is a cross sectional view of molding apparatus for forminga rounded edge contact lens in accordance with a method of the presentinvention.

DESCRIPTION OF THE PRESENT INVENTION

[0030] New methods for cast molding contact lenses have been discovered.The present invention provides the ease of cast molding with the abilityto produce a substantially smooth, rounded edge forms or surfaceswithout the need for costly post-processing steps.

[0031] Conventional cast molding techniques for manufacturing fully castmolded lenses produce a lens with a sharp, pointed edge profile. Asmentioned hereinabove, the sharp edge is sometimes made to be smoothedor rounded by means of a polishing step that is separate from the castmolding process.

[0032] Turning now to FIG. 1A, two conventional mold halves 20, 30 whichare sometimes hereinafter referred to as “casting cups”, are shown incross-section, as assembled together during conventional cast moldingtechniques. Lens material, for example a curable, mixture ofpolymerizable monomers, is introduced into a lens-shaped cavity 40defined between the casting cups 20, 30 to form the fully cast moldedlens product.

[0033] Any suitable lens material or lens material precursor may beemployed in forming the present contact lenses and lens bodies inaccordance with the present invention. The final contact lens and lensbody may be rigid, rigid gas permeable, soft, and/or hydrophilic.Preferably, the contact lens or lens body, for example, hydrated foruse, is soft and in the form of a hydrogel and/or a high oxygenpermeability, that is a high Dk, material. One particularly useful classof lens materials are hydrophilic silicone-containing materials. Suchhydrophilic silicone-containing materials are high Dk materials and mayhave a number of the advantageous properties of both silicone polymericmaterials, for example, crosslinked silicone polymeric materials, andhydrogel-forming polymeric materials. Contact lenses made of hydrophilicsilicone-containing materials often have a relatively high modulus andare very advantageous, for example, provide reduced risk of eyeirritation, when structured to include a rounded peripheral edge form orsurface, in accordance with the present invention.

[0034] In the example shown in FIG. 1, one casting cup 20 generallydefines a negative impression of the lens back or posterior surface(base curve) and one casting cup 30 generally defines a negativeimpression of the lens front or anterior surface.

[0035] In commercially available lenses, the point at which the two moldhalves meet is usually chosen as the outer periphery of the finishedlens. As shown in FIG. 1A, the mold cups 20, 30 meet at a point 50. Thispoint 50 generally defines the molded lens edge. The edge of a fullymolded lens conventionally represents the split line 60 between the maleand female casting cups 20, 30.

[0036] Another example of such a conventional arrangement is shown inFIG. 1B, with back surface mold section 70 and front mold section 80forming cavity 90, and point 100 defining the lens periphery.

[0037] It can therefore be seen that conventional molding techniquesproduce a lens with a lens edge form which is “chiselled”, or “pointed”.Typical lens profiles formed by conventional cast molding techniques areshown in FIGS. 2A, 2B, 2C and 2D.

[0038] In contrast, as will now be described, the methods of the presentinvention produce a substantially smooth, rounded edge profile. Acontact lens 110 formed by a method in accordance with the presentinvention is shown in FIG. 3.

[0039] Importantly, the illustrated lens 110 is produced in the fullymolded state, without post molding steps designed to alter the shape orconfiguration of the peripheral edge. As shown, the lens 110 produced bya method in accordance with the present invention has a rounded, smoothedge 112.

[0040] Although the lens 110 may have seen some of the processing stepsconventionally associated with a lens of this type, for example,demolding, hydration, inspection, packaging and sterilization, the lens110 edge profile has not been substantially altered from its original,molded shape.

[0041] The illustrated lens 110 is produced by modification to inserttooling which is conventionally used to create the casting cups (i.e.mold halves) that are used to cast mold the lens.

[0042] As is well known in the art, prior to the cast molding of thecontact lens, each of the mold sections (such as back surface mold 20and front surface mold 30 in FIG. 1), is formed by injection molding aresin in the cavity of an injection molding apparatus. Mounted in theinjection molding apparatus are “tools” (hereinafter sometimes referredto as “tooling inserts”) for forming the optical surface impressions onthe mold sections. Whereas the mold sections are typically used onlyonce for casting an individual lens, the injection molding tools areused to make hundreds of mold sections (i.e. mold halves).

[0043] The tools used to make the mold sections are manufactured toextremely high specifications. No roughness or other surface defects areacceptable on a tool as such defects would be transferred to all of themold sections made therefrom. Any such defect on the mold sectionsurface would be transferred to the molded contact lens. The tools aretypically made from brass, stainless steel, nickel or some combinationthereof.

[0044] Turning now to FIGS. 4A and 4B, a conventionally manufacturedtool 120 is shown.

[0045] Typically, for making the back surface mold (such as mold half 20shown in FIG. 1A), the tool 120 includes at least one base curve(represented by line 122), to provide fit and/or refractive correction,the correction being, for example, spherical, torodial, multifocal,bifocal, etc. In addition, the tool 120 includes a feature 124 whichforms part of the lens edge geometry. Feature 124 is sometimes tapered.The edge tapering on the back surface tool is conventionally flat orconcave, in order to achieve a taper on the edge of the molded lens.

[0046] In other conventional tools (not shown) the edge feature 124 isomitted from the tool and the base curve is run out to the lensperiphery. For example, the back surface tool may have no defined edgefeature other than the base curve itself. In this case, edge tapering ofthe molded lens is usually accomplished by the surface profile of thefront surface mold tool which includes a tapered edge feature.

[0047]FIG. 5 shows a cross sectional view of a lens 150 produced in thismanner, i.e. in which base curve (represented in part by phantom line152) is run out to the lens periphery 154 and no edge feature has beenprovided on the back surface tool (not shown). As can be seen, the lensedge geometry that this technique yields is also pointed, such as thelenses shown in FIGS. 2A-2D.

[0048] It will be appreciated by those skilled in the art that atsufficiently high magnification, the sharp, angular corners of thelenses shown in FIGS. 2A-2D and FIG. 5 may well be slightly curved orradiused, due to shrinking in the mold for example, and therefore themolded lenses may not precisely duplicate the tooling insert geometry.However, the edge profile of the fully molded lenses shown are sharp andangular, and moreover, do not represent a more desirable, roundedprofile that have been only conventionally available only in machinedlenses or cast molded lenses which have undergone post processingpolishing to alter, e.g., round, the peripheral edge of the lens.

[0049] As is described elsewhere herein, a method for cast molding acontact lens in accordance with the present invention generallycomprises the steps of providing a back surface tool having a surfacecorresponding to a desired contact lens surface and at least one convexcurve along an outer radius thereof, positioning the tool in a moldingapparatus, for example, a conventional injection molding apparatus,introducing a moldable material into the molding apparatus andsubjecting the material to conditions, for example, chosen fromconditions conventionally used, effective to form a first mold sectionhaving a negative impression of the surface of the tool, assembling thefirst mold section with a second mold section to form a lens shapedcavity therebetween, and forming a contact lens member having a roundededge form in the lens shaped cavity of the assembled mold sections. Upondemolding, the contact lens member itself is the contact lens product,or can be subjected to hydration to provide the contact lens product.

[0050] More particularly, referring now to FIGS. 6-8, in contrast to theconventionally cast molded lenses, the present invention purposefullyplaces at least one convex radius, or curve, at the outer or peripheraledge of a back surface tooling insert. This convex radius can begenerated by a series of flats, for example, very short flats whichtogether closely simulate continuously curved convex shaping, or by acombination of flats and convex curves, on the tooling insert.

[0051] Referring now specifically to FIGS. 6 and 7, in one embodiment ofthe present invention, a tooling insert 160 is provided. The toolinginsert 160 having such convex shaping as generally describedhereinabove. For the lens 110 manufactured in accordance with thepresent invention and shown in FIG. 3, the tool 160 used in themanufacture of the lens 110 includes a convex curve along its outerradius, or peripheral edge surface 162.

[0052] Unlike prior tooling inserts that have been used in themanufacture of conventionally cast molded lenses, the present inventionprovides a method for manufacturing a contact lens having a cast molded,convex curved radius at the lens edge periphery.

[0053] Referring now as well to FIG. 8, a portion of an assembledcasting cup pair 164 for fully cast molding a rounded edge contact lensin accordance with the present invention is shown. The cup pair 164comprises a first, back surface mold half 166 assembled with a second,front surface mold half 168. The convex outer radius of the tool 160used to make the back surface mold half 166 may be about 0.05 mm radiusor larger.

[0054] When the mold halves 166, 168 are assembled together, the finalfully cast molded lens, such as lens 110, has a substantially smooth,rounded edge as shown. Using a convex curve on the portion of the backsurface tool 160 that creates the lens periphery can be used to yield alens with a much more rounded shape, such as seen in the lens 110 ofFIG. 3.

[0055] Preferably, when the two mold halves 166, 168 are assembled, theangle of intersection (represented by symbol a in FIG. 8) of the molds166, 168, on the lens side, is greater than about 100 degrees. In thecase of the lens 110 shown in FIG. 3 the angle of intersection of thetwo mold halves, on the lens side, is 140 degrees on the unprocessed orunhydrated lens member, in the dry state, producing a final or hydratedcontact lens 110 with a much more rounded or less clearly defined edgesurface. It is to be appreciated that the angle of intersection of thetwo mold halves on the lens side could be made less than or greater thanabout 140 degrees, for example, angles greater than 100 degrees could beused, for example, in the range of about 100 degrees to about 170degrees or more.

[0056] After assembling the mold halves 166, 168, the rounded edgedcontact lens can be cast molded using conventional steps as known tothose skilled in the art and described hereinabove. Although it isappreciated that processing steps performed after the cast molding, forexample hydration, in the case of a hydrogel hydrophilic lenses, may tosome extent change the finished lens manufactured in accordance with thepresent invention, the peripheral edge form of the finished lens remainssubstantially unaltered and much smoother than the conventional‘chiseled’ edge previously seen.

[0057] By implementation of the present invention, a fully cast moldedlens can be created with the desired (rounded) edge, without the needfor dedicated post formation polishing and machining steps to create thedesired peripheral edge form.

[0058] Although there has been hereinabove described specific methods ofmanufacturing a rounded edge contact lens having a rounded peripheraledge surface or form, in accordance with the present invention, for thepurpose of illustrating the manner in which the invention may be used toadvantage, it should be appreciated that the invention is not limitedthereto. Accordingly, any and all modifications, variations, orequivalent arrangements which may occur to those skilled in the art,should be considered to be within the scope of the present invention asdefined in the appended claims.

What is claimed is:
 1. A method for producing a contact lens, the methodcomprising: providing a back surface tool having a surface generallycorresponding to a desired contact lens surface and a convex curve alongan outer radius thereof; positioning the tool in a molding apparatus;introducing a moldable material into the molding apparatus andsubjecting the moldable material to conditions effective to form a firstmold section having a negative impression of the surface of the tool;assembling the first mold section with a second mold section to form alens shaped cavity therebetween; and forming a contact lens member inthe lens shaped cavity of the assembled mold sections.
 2. The method ofclaim 1 wherein the contact lens member formed has a rounded edge. 3.The method of claim 1 which further comprises demolding the contact lensmember and hydrating the contact lens member to form a contact lenshaving a rounded edge.
 4. The method of claim 1 wherein the lens shapedcavity defines a junction angle on a lens side between the assembledmold sections, the junction angle being at least about 100 degrees. 5.The method of claim 1 wherein the lens shaped cavity defines a junctionangle on a lens side between the assembled mold sections, the junctionangle being in the range of about 100 degrees to about 170 degrees. 6.The method of claim 1 wherein the first mold section is a back surfacemold section for forming a posterior surface of the contact lens.
 7. Themethod of claim 1 wherein the convex curve along the outer radius of thesurface is at least about 0.05 mm in radius.
 8. The method of claim 1wherein the forming step comprises polymerizing a lens formingcomposition in the lens shaped cavity.
 9. A mold useful in producing acontact lens comprising: a first mold section having a surface in ageneral shape of a negative of a posterior face of a contact lens and aconcave outer edge surface; a second mold section having a surface in ageneral shape of a negative of an anterior face of the contact lens; andthe first mold section and the second mold section being adapted to beassembled together to define a cavity.
 10. The mold of claim 9 whereinthe cavity is in a general shape of a contact lens having a roundededge.
 11. The mold of claim 9 wherein the cavity defines a junctionangle on a lens side between the assembled mold sections, the junctionangle being at least about 100 degrees.
 12. The mold of claim 9 whereinthe cavity defines a junction angle on a lens side between the assembledmold sections, the junction angle being in the range of about 100degrees to about 170 degrees.
 13. The mold of claim 9 wherein theconcave outer edge surface of the first mold section has a radius of atleast about 0.05 mm.
 14. A tool useful in making a mold section for castmolding a contact lens, the tool comprising: an insert adapted to beplaced in a molding apparatus in forming a first mold section having anegative impression of a surface of the tool, the surface of the toolincluding a first surface portion in the general shape of a posteriorface of a contact lens and a second surface portion defining a convexcurved outer peripheral edge surface of the insert.
 15. The tool ofclaim 14 wherein the convex curved outer peripheral edge surface of theinsert has a radius of at least about 0.05 mm.
 16. The tool of claim 14wherein the convex curved outer peripheral edge surface of the insert iscreated by a series of flats approximating a convex curve.
 17. Themethod of claim 14 wherein the convex curved outer peripheral edgesurface of the insert is created by a combination of flats and convexcurves.
 18. A contact lens sized and adapted for placement on a corneaof an eye, the contact lens comprising: a lens body having an anteriorface, a posterior face and an outer peripheral edge surface extendingfrom the anterior face to the posterior face and having a roundedconfiguration, the lens body formed by a process including cast moldingusing a first mold section having a surface in a general shape of anegative of the posterior face and a concave outer edge surface, and asecond mold section having a surface in a general shape of a negative ofthe anterior face, the lens body being subjected to no post-formationprocessing to alter the rounded configuration of the outer peripheraledge surface.
 19. The contact lens of claim 18 wherein the lens bodycomprises a material selected from the group consisting ofhydrogel-forming polymeric materials and mixtures thereof.
 20. Thecontact lens of claim 18 wherein the lens body comprises a hydrophilicsilicone-containing material.